For many high temperature applications, such as high temperature insulation, it is desirable to have a densified felt, blanket or batting structure which will retain its integrity and its dense structure at prolonged exposure to high temperatures. Structures are desirable which can be used at temperatures greater than 400 degrees C. and which will maintain their good mechanical and physical characteristics.
Elongatable carbonaceous fibers described in copending U.S. patent application Ser. No. 112,353 of McCullough et al, which is herewith incorporated by reference, and the insulation material described in copending U.S. patent application Ser. No. 108,255 of McCullough et al, offer good base materials for high temperatures applications. However, it has not been possible, prior to the present invention described hereinafter, to permanently densify the batting structures described in the above patent applications and maintain their integrity at high temperatures.
For example, in U.S. patent application Ser. No. 114,324 of McCullough et al, there is described blending non-flammable p-aramid fibers with the carbonaceous fibers described in U.S. patent application Ser. No. 112,353 and using a needle punch to densify the structure. However, at temperatures greater than 400 degrees C. the p-aramid decomposes and the batting looses its integrity. It is therefore a considerable advantage to be able to permanently lock a densified batting together with material which does not lose its physical properties at elevated temperatures.
U.S. Pat. No. 4,628,846 to Vives, which is incorporated herein by reference, discloses an apparatus which may be utilized to prepare the fibrous structures of the invention.
U.S. Pat. No. 4,284,680 to Awano et al discloses a multi-layered needle point felt-like cushioning material which is prepared by needle punching battings to a foundation fabric and heating to set the fibers of the batts. However, the fibers are not stabilized and heating is performed in air at temperatures wherein only a temporary set occurs.
It is understood that the term "implanting" as utilized in the present application relates to entangling, intermingling, interlocking, or the like, of the fibers.
The term "structure" as used herein generally relates to one or more plies of a mat, batting, felt or blanket. The structure may or may not be provided with one or more scrims.